1. Field of the Invention
This invention relates to a die with controlled breather for use in rotational pressing.
2. State of the Prior Art
In rotational pressing it is indispensable to apply on the dies a breather whose purpose is to maintain atmospheric pressure inside the die during the pressing process. Indeed, if the die were completely closed during the heating step there would be an increase in pressure which might cause escape of material through the flanges or breakage of the die. In addition, during the cooling step there might be a pressure decrease which would generate air sucked through the flanges of the die or a deformation of the part.
The breather is usually a simple hole, often with a tube, which puts the interior of the die in communication with the external environment. To avoid material coming out of this hole during pressing, filters are inserted, very often consisting of steel wool.
During the initial step of pressing the still powdered plastic material ends up by depositing on the filter, then melting and solidifying during cooling. This leads in a short time to obstruction of the breather.
Management of these breathers is entrusted to an operator who at each pressing cycle must clean the breather and replace the filters. Negligence in this operation leads to obstruction of the breather with resulting defects in the pressed part or damage of the die.
The general purpose of this invention is to remedy the above-mentioned shortcomings by making available a more efficient breather system with innovative characteristics.